A major part of the investigation is based on determining the action spectra; that is identification of the wavelengths of ultraviolet light, visible and infrared radiation and the minimum intensity of radiation that will produce changes in the skin. This is determined by irradiating the skin with narrow wavebands, usually 4 nm wide, of measured intensity. The light source used is either a 2.5 KW xenon or xenon-mercury lamp; monochromatic radiation is obtained with a prism grating monochromator designed to reduce stray radiation but give sufficiently high output for irradiating patients within a relatively short time. The investigator has studied a variety of photo-dermatoses, drug sensitivity, photoallergy to topical chemicals, lupus erythaematosus, xeroderma pigmentosa, polymorphous light eruption, Bloom's syndrome, various forms of porphyria and solar urticaria. Biological systems irradiated include selective killing of T lymphocytes with preservation of B lymphocytes with ultraviolet radiation and action spectra of topically applied and oral psoralens, hepatic pathology of erythropoietic protoporphyria and comparisons with animal experimental models. Clinical and porphyrin studies of more than 120 different types of porphyria; not including a study of prophyria turcica (hexachlorobenzene intoxication) twenty years after, made on a site visit in Turkey in May, 1977, in which clinical observation, porphyrin determination, HCB levels in tissue were made.